CHARACTERIZATION AND MODELING OF LOW-FIELD N-CHANNEL MOSFETS INVERSION-LAYER MOBILITY AT TEMPERATURES ABOVE 300 K

We have studied the electron effective mobility in the inversion layer s of n-channel MOSFETs fabricated in our laboratory as a function of g ate electric field and temperature and have also analyzed the transver se field and temperature dependence of channel mobility obtained by ot her workers. These investigations have revealed that for low doped sub strates and high temperatures, scattering is dominated by bulk and sur face phonon modes and the effective mobility can be modelled by combin ing the two mechanisms using Matthiessen's rule. The phonon dominated mobility shows a universal dependence on the effective transverse fiel d (E-eff) which can be expressed as mu(eff) = mu(o) (E-c/E-eff)(sigma) . We have verified the validity of this relation above 300 K by incorp orating appropriate temperature dependences for mu(o) and sigma. The m odal calculations have been compared with the experimental results on a number of devices fabricated under different processing conditions. Good agreement between the modelled and experimental results is observ ed at all temperatures up to E-eff values of about 4 x 10(5) V/cm. At higher fields surface roughness scattering becomes important and mobil ity starts degrading faster with the effective field. The current volt age characteristics of MOSFETs generated using the proposed mobility m odel have also shown good agreement with the measured values of drain current at different temperatures.